1. Field of the Invention
The present invention relates to transmission assemblies, gear change devices and dynamic components utilized for transferring power and torque. More specifically, the present invention pertains to an improved transmission assembly that utilizes a plurality of axially floating countershafts that adjust to equally accept input load for preventing excessive wear, improving component lifespan and reducing potential harmonics due to unequal load-sharing between transmission countershaft members. The present invention further provides equal load-share while incorporating gear change synchronizers to facilitate smooth gear changes while preventing excessive wearing of these components due to radial positioning mismatch or slack.
Automotive and other vehicle transmissions are well known for transmitting and transforming input power from a rotary power source into one that is suitable for desired output, whether driving the wheels of the vehicle or operating a mechanical component in a manufacturing process. The goal is generally to create an efficient and reliable dynamic assembly that can accept considerable loads without occupying undue space, consuming energy or reducing the effectiveness of the overall process. To effectively transmit high levels torque, most transmissions utilize intermediate shafts to split the torque into different paths using smaller elements, which permit designers to reduce the overall size of the individual components over a design utilizing a single transmission pathway subjected to the entirety of the torque input load. By splitting the torque, the structural requirements of the components are reduced, where otherwise a single shaft would require significant load carrying capacity for the same end goal. The use of several countershafts, in particular, splits the load between several gear components and intermediate shafts, which increases the number of components in the assembly but can significantly reduce their individual size. Thus efficient placement and spacing of components allows the overall transmission to be reduced in size when compared to the size requirements of larger transmission components using fewer or no load splits.
The primary concern related to separating a transmission input load and distributing it to several intermediate elements is the potential for imbalanced load transfer and uneven contact between meshed gear sets. A perfectly meshed set of components can be designed, but the reality of design tolerances and manufacturing and assembly considerations inevitably leads to mismatches in contact between these components, which are further exacerbated by their dynamic nature. Unequal contact and unequal load share can result in excessive wear, reduced component life, premature failure of the system and harmonics that threaten the operation of the transmission. Uneven wear and complete failure from this unequal load share creates an obstacle to efficiently separating input load into intermediaries without compromising longevity.
The present invention is provided as an improved transmission assembly having countershafts that are capable of utilizing gear synchronizers and further for allowing equal distribution of load between an input shaft and a plurality of countershafts. Most conventional twin and multiple countershaft transmissions achieve equal load sharing between countershafts by allowing free radial movement of main shaft and main shaft gears to account for the imbalance. There are a lot of advantages to this design and it has been shown to be highly effective and widely implemented for vehicle transmission assemblies; however the main drawback to this design is the inability to utilize gear synchronizers, as the radial movement of the gears causes nonuniform contact and increased friction between the synchronizer ring and the cone surface of the main shaft gears when shifting. This friction results in reduced reliability and useful life of the synchronizer, as the friction rapidly creates wear and premature failure. It will be appreciated then that the ability to utilize synchronizers in a transmission having radially floating members precluded, and therefore the overall shifting quality is reduced for the user during gear transitions.
Specifically, the present invention provides a transmission having a plurality of countershafts that are fixed radially and allowed to float axially to account for torque mismatch between complementary countershafts when countershaft gears are in contact with main shaft gear. The countershafts are adapted to displace axially in either direction to account for uneven load transfer, wherein the countershaft gears are helical gears having the same helix hand. When shifting to one gear, the constant gear and ongoing engaged gear on countershaft will automatically self-adapt or self-adjust while balancing any axial load imbalance between the countershafts. The constant gear set and ongoing engaged gear set will then mesh each other to achieve equal load sharing, as the helical gear teeth transform the torque into an axial load, which is balanced between the set of countershafts.
2. Description of the Prior Art
Many transmission systems and gear change mechanisms have been disclosed in the prior art that relate to equal load share between transmission countershaft and main shaft members. These include devices that have been patented and published in patent application publications, and generally relate to radially floating members or designs that include a balancing means. The forgoing is a list of devices deemed most relevant to the present disclosure, which are herein described for the purposes of highlighting and differentiating the unique aspects of the present invention, and further highlighting the drawbacks existing in the prior art.
Specifically, U.S. Pat. No. 4,640,145 to Vandervoort discloses a multiple countershaft transmission assembly that is designed to reduce to the overall noise signature of the device during operation, as a gear tooth meshing and surface contact noises is mitigated through its unique design. Specifically, the assembly comprises a gear change transmission having multiple countershaft assemblies, wherein an input gear is constantly engaged with a countershaft gear. The input gear is provided having a gear tooth pitch that is not evenly divisible by the number of countershafts, whereby there is a time interval between gear meshing between the input and countershaft to reduce noise generation. The contact noise is not amplified but rather offset between countershafts. The Vandervoort transmission assembly, while providing a unique, lower noise transmission does not include synchronizer and a means of offsetting countershaft engagement with respect to an input shaft to reduce overall input and output shaft displacement, as provided for in the present invention.
Another such device is U.S. Pat. No. 4,807,493 to Loeffler, which discloses a twin countershaft transmission assembly having a floating main shaft having no internal or external bearings or other support device near its adjacent ends, whereby the main shaft is supported by a gears carrying the torque thereto. This arrangement provides a true torque split between countershafts, as the main shaft is able to accommodate relative movement between the shafts by not being constrained by a bearing or support device. The Loeffler device discloses a transmission having a self-aligning main shaft, while the present invention provides an even torque split and reduced component wear by allowing lateral displacement of the countershafts along their length to accommodate relative input and output shaft movement.
U.S. Pat. No. 3,611,823 to Richards discloses a similarly designed transmission assembly as that of Loeffler, wherein a transmission having a floating input or main drive gear is provided that freely displaces in an axial direction relative to both the input shaft and to the transmission main shaft. A coupling member linking the input shaft and the input gear permits axial rocking movement of the input gear relative to the input shaft to maintain alignment and identically rotate countershafts at substantially identical speeds. The Richards device, similar to the Loeffler device, fails to disclose axially adjusting countershafts that accept input from the input shaft without creating stress concentrations, binding, or other wearing situations otherwise created when the input and output shaft displace radially and unequally distribute torque to the countershafts. The present invention provides an axially adjusting set of countershafts to maintain even contact between the input and all meshed countershafts within the transmission assembly.
U.S. Pat. No. 6,073,506 to Wireman discloses a multiple countershaft transmission that includes at least two countershafts having sufficient gear tooth backlash such that the countershafts not presently transmitting drive torque due to minor assembly imperfections do not to impede substantially equal load-sharing of those countershafts transmitting drive torque. In this way, the Wireman device includes a means of maintaining equal load-sharing between countershafts in spite of assembly and manufacturing imperfections that cause unequal contacts within the transmission assembly. The backlash provides sufficient clearance for imperfections between a plurality of meshed gears, which are inevitably unequally in their contact between meshed pairs and lead to unequal torque distribution. The Wireman device intends to include greater tolerances between gear sets, as opposed to the present invention that provides an axially displacing countershaft design that accommodates unequal contact intervals and unequal load-sharing from a driving gear to the countershaft gears.
U.S. Pat. No. 4,709,590 to Richards discloses a change speed gear transmission having a plurality of spaced countershafts and countershaft gears thereon, a driving and driven means for rotating the countershafts, a central shaft and gears and a clutch means. The gears of the transmission are double-helical gears that assure that the load transmitting gear will tend to automatically self-align into a position where each countershaft transmits substantially equal torque load. Similar to the Wireman device, the Richards device includes a new gear design that attempts to solve unequal load sharing. The present invention provides axially adjustable countershaft gears to account for unequal load sharing between several countershafts from a driving input.
Finally, U.S. Pat. No. 6,374,689 to Morrow discloses a load balancing gear set apparatus that utilizes a balancing mechanism to deliver equal and optimum power to intermediate shafts within the transmission. The transmission includes a power input and pairs of intermediate elements that engage using helical gear sets. To obtain even power distribution between intermediate elements from the input, a mechanical balancing element comprising a lever mechanism mounted to a pivot point is provided, wherein the lever mechanism is permitted a rocking motion that displaces the intermediate shafts in the presence of load imbalance. Imbalanced loads in helical gears create axial loads that will pivot the lever mechanism into an equilibrium position. This design, while simple and effective for balancing countershaft transmission elements, requires a common lever mechanism to operate, and may not function with many countershafts beyond a simple pair. The present invention is adapted to allow free axial movement of each countershaft to balance these loads, wherein each countershaft is free to move independently based on input load displacing the countershafts into a state of equal load sharing.
The present invention provides an improved gear change mechanism and transmission that incorporates axially floating countershafts to account for load mismatch and further allow for the use of synchronizers for smooth gear transitions. It is submitted that the present invention is substantially divergent in design elements from the prior art, and consequently it is clear that there is a need in the art for an improvement to existing countershaft transmission devices. In this regard the instant invention substantially fulfills these needs.